The crystalline differences could come as a result of oxygen, Yufeng Hao of University of Texas at Austin and colleagues report October 24 in Science. The scientists found that larger graphene crystals with branched edges grew faster on copper surfaces exposed to oxygen for longer time periods. Copper surfaces with fewer oxygen atoms sprouted smaller, more compact graphene crystals with sharp edges.

Controlling the oxygen exposure, along with other variables such as temperature and pressure, of the copper surfaces could allow scientists to grow larger, more uniform graphene crystals, which may work better in electronic devices and other applications.